WO publication 98/54052 discloses a ship with twin propellers and twin Schilling rudders; i.e., a respective rudder for each propeller. Each rudder is pivotably mounted by a respective shaft, has a bulbous nose portion, a wasted mid-portion and a flared tail. The flared tail flares outwardly substantially only on the inner side of each rudder; i.e., the side which faces the other rudder pair.
Each rudder has an upper plate and a lower plate with the plates much more extensive on the inner side than on the outer side, the plates being aligned with streamlines from the respective propeller and the lower plate having a downwardly angled portion on the inner side. The rudders seem to form some kind of a toe-out angle in relation to the centerline of the hull.
U.S. Pat. No. 7,033,234 discloses a method for steering a planning V-bottomed boat with double individually steerable drive units with underwater housings, which extend down from the bottom of the boat. When running at planning speed straight ahead, the underwater housings are set with a so called toe-in angle; i.e., inclined towards each other with opposite angles of equal magnitude relative to the boat center line. When turning the boat, the inner drive unit is set with a greater steering angle than the outer drive unit.
JP Patent Publication 2006007937 discloses an arrangement in a ship with two pods with contra-rotating propellers situated at the stern of the ship. The first pod is in a first embodiment mounted stationary into the skeg so that the shaft line is inclined upwards. The second pod is fastened by a horizontal axis to a steering table, which steering table rotates around a vertical axis and which steering table can be lowered and raised by hydraulic cylinders. The shaft line of the second pod is aligned with the shaft line of the first pod. The rear end of the first pod is in a second embodiment fastened with a horizontal axis to the skeg and the front end of the first pod is fastened to a vertical cylinder. The inclination of the first pod can thus be adjusted with the cylinder. Both pods are in a third embodiment fastened to opposite ends of a common frame, which frame is supported from the middle part a horizontal axis to a steering table, which steering table rotates around a vertical axis and which steering table can be lowered and raised by hydraulic cylinders. There is no separate rudder in this arrangement and the steering of the ship is done by rotating either only the second pod situated after the first pod in the driving direction of the ship around a vertical axis or by rotating both pods around a vertical axis.